The present invention is generally directed to toner processes, and more specifically, to aggregation and coalescence processes for the preparation of toner compositions. In embodiments, the present invention is directed to the economical preparation of toners without the utilization of the known melt mixing, pulverization and/or classification methods, and wherein in embodiments toner compositions, or toner with an volume average diameter of from about 1 to about 25, and preferably from 1 to about 10 microns, and narrow GSD of, for example, from about 1.16 to about 1.26 as measured on the Coulter Counter can be obtained. The resulting toners can be selected for known electrophotographic imaging, printing processes, including color processes, and lithography. Specifically, with the processes of the present invention there is selected a stabilizer comprised of solid particulants, and more specifically, a submicron tricalcium phosphate particulant suspension in water is added after the aggregation of latex particles with the pigment particles, and prior to the coalescence of the toner aggregates, and wherein the particle size of the toner aggregates, and the GSD of the toner aggregates are retained over a wide range of temperatures, and wherein in embodiments there is enabled a process reduction time of from about 40 to about 75 percent. The present invention in embodiments is directed to a process for the preparation of toner particles comprising
(i) preparing a pigment dispersion comprised of a pigment finely dispersed in a nonionic surfactant, an added ionic surfactant, preferably a cationic surfactant, and optionally other additives; PA1 (ii) shearing the pigment dispersion with a latex or emulsion blend comprised of submicron resin particles, a counterionic surfactant, such as an anionic surfactant, and a nonionic surfactant using a high speed rotor-stator device such as a polytron; PA1 (iii) heating the above sheared blend to a temperature below the glass transition temperature (Tg) of the resin to form electrostatically bound toner size aggregates with a narrow particle size distribution; PA1 (iv) followed by adding a stabilizer preferably of in situ tricalcium phosphate solid particulants or particles preferably generated from an aqueous solution of calcium chloride and trisodium phosphate; PA1 (v) heating the resulting mixture (iv) above the Tg of the resin to coalesce the aggregates to form toner particles comprised of resin, pigment and optional additives; followed by PA1 (vi) washing the toner particles with an acid, such as nitric acid, for example one molar nitric acid, or dilute nitric acid, to dissolve the tricalcium phosphate; and followed by PA1 (vii) washing with water and drying the said toner particles. PA1 (i) preparing a latex emulsion by agitating in water a mixture of a nonionic surfactant, an anionic surfactant, a first nonpolar olefinic monomer, a second nonpolar diolefinic monomer, a free radical initiator and a chain transfer agent; PA1 (ii) polymerizing the latex emulsion mixture by heating from ambient temperature to about 80.degree. C. to form nonpolar olefinic emulsion resin particles of volume average diameter of from about 5 nanometers to about 500 nanometers; PA1 (iii) diluting the nonpolar olefinic emulsion resin particle mixture with water; PA1 (iv) adding to the diluted resin particle mixture a colorant or pigment particles and optionally dispersing the resulting mixture with a homogenizer; PA1 (v) adding a cationic surfactant to flocculate the colorant or pigment particles to the surface of the emulsion resin particles; PA1 (vi) homogenizing the flocculated mixture at high shear to form statically bound aggregated composite particles with a volume average diameter of less than or equal to about 5 microns; PA1 (vii) heating the statically bound aggregate composite particles to form nonpolar toner sized particles; PA1 (viii) halogenating the nonpolar toner sized particles to form nonpolar toner sized particles having a halopolymer resin outer surface or encapsulating shell; and PA1 (ix) isolating the nonpolar toner sized composite particles. PA1 (i) preparing or providing a pigment dispersion comprised of a pigment dispersed in an ionic surfactant; PA1 (ii) shearing the pigment dispersion with a latex or emulsion blend comprised of submicron, for example less than about one micron, resin particles and a counterionic surfactant; PA1 (iii) heating the above sheared blend below the glass transition temperature (Tg) of the resin to form electrostatically bound toner size aggregates; PA1 (iv) adding a stabilizer of in situ tricalcium phosphate (TCP) solid particulants generated from a solution of calcium chloride and trisodium phosphate; PA1 (v) heating the mixture of (iii) and (iv) above about the Tg of the resin to obtain toner size particles comprised of resin and pigment; PA1 (vi) washing with an acid to dissolve the TCP; and PA1 (vii) washing with water and drying the toner obtained. PA1 (i) preparing a pigment dispersion comprised of a pigment finely dispersed in a nonionic surfactant to which is added an ionic surfactant, preferably a cationic surfactant, and optional additives; PA1 (ii) shearing the pigment dispersion with a latex mixture comprised of submicron resin particles in water and counterionic surfactant, such as an anionic surfactant, and a nonionic surfactant; PA1 (iii) heating the resulting homogenized mixture below the resin Tg at a temperature of from about 35 to about 50.degree. C. (or 5 to 15.degree. C. below the resin Tg) thereby causing flocculation or heterocoagulation of the formed particles of pigment, resin and optional additives to form electrostatically bounded toner size aggregates; PA1 (iv) followed by the addition of in situ submicron tricalcium phosphate solid particulate generated from an aqueous solution of calcium chloride and trisodium phosphate; PA1 (v) heating to, for example, from about 60 to about 95.degree. C. the statically bound aggregated particles of (iv) to form the toner particles comprised of polymeric resin and pigment; and PA1 (vi) followed by washing with a dilute acid, and by washing with water and drying of the toner particles. PA1 (i) preparing a pigment dispersion in water, which dispersion is comprised of a pigment of a diameter of from about 0.01 to about 0.5 microns in volume average diameter, an ionic surfactant, such as a cationic, and optional additives, such as charge control agents or release agents; PA1 (ii) shearing the pigment dispersion with a latex blend comprised of resin particles of submicron size of from about 0.01 to about 0.5 micron in volume average diameter, a counterionic surfactant such as an anionic surfactant, and a nonionic surfactant thereby causing a flocculation or heterocoagulation of the formed particles of pigment, resin and optional additives to form a uniform dispersion of solids in the water and surfactant system; PA1 (iii) heating the above sheared blend at a temperature of from about 5 to about 15.degree. C. below the Tg of the resin particles while continuously stirring to form electrostatically bound or attached relatively stable (for Coulter Counter measurements) toner size aggregates with a narrow particle size distribution; PA1 (iv) followed by the addition of aqueous submicron tricalcium phosphate particulate stabilizer generated in an in situ manner from aqueous calcium chloride and trisodium phosphate using a high shearing device such as a polytron operating at speeds of 5,000 to 15,000 rpm; PA1 (v) heating and coalescing the statically bound aggregated particles at a temperature of from about 5 to about 35.degree. C. above the Tg of the resin to provide mechanically stable toner particles comprised of polymeric resin, pigment and optional additives; PA1 (vi) washing the toner particles with an acid, followed by water washes; PA1 (vii) separating the toner particles from the water by filtration; and
In embodiments, the present invention is directed to a process comprised of dispersing a pigment and optionally toner additives like a charge control agent or additive in an aqueous mixture containing an ionic surfactant, such as cationic surfactant, in amounts of from about 0.5 percent (weight percent throughout unless otherwise indicated) to about 10 percent, and shearing this mixture with a latex or emulsion mixture comprised of suspended submicron resin particles of from, for example, about 0.01 micron to about 1 micron in volume average diameter in an aqueous solution containing a counterionic surfactant, such as anionic surfactant in amounts of from about 1 percent to about 10 percent, and nonionic surfactant in amounts of from about 0.1 percent to about 5 percent, thereby causing a flocculation of resin particles, pigment particles and optional additives, such as CCA (charge control additive) or release agents, followed by heating at about 5 to about 40.degree. C. below the resin Tg and preferably about 5 to about 15.degree. C. below the resin Tg while stirring of the flocculent mixture which is believed to form statically bound aggregates of from about 1 micron to about 10 microns in volume average diameter, comprised of resin, pigment and optionally additives, adding a stabilizer of submicron in situ tricalcium phosphate (TCP) solid particulants suspended in water, and thereafter heating the TCP stabilized aggregates to a temperature above the Tg (glass transition temperature) of the resin. The size of the aforementioned statistically bonded aggregated particles can be further controlled by adjusting the temperature in the aggregation step. An increase in the temperature causes an increase in the size of the aggregated particle. This process of aggregating submicron latex and pigment particles is kinetically controlled, that is the temperature increases the process of aggregation. The higher the temperature during stirring, the quicker the aggregates are formed, for example from about 2 to about 10 times faster in embodiments, and the latex submicron particles are picked up more quickly. The temperature also controls in embodiments the particle size distribution of the aggregates, for example the higher the temperature the narrower the particle size distribution, and this narrower distribution can be achieved in, for example, from about 0.5 to about 24 hours and preferably in about 1 to about 3 hours time. Heating the mixture about above or in embodiments equal to the resin Tg generates toner particles with, for example, an average particle volume diameter of from about 1 to about 25 and preferably 10 microns. It is believed that during the heating stage, the components of aggregated particles fuse together to form composite toner particles. In another embodiment thereof, the present invention is directed to an in situ process comprised of first dispersing a dry or wet cake of pigment, such as HELIOGEN BLUE.TM., or HOSTAPERM PINK.TM., in an aqueous mixture containing a cationic surfactant, such as benzalkonium chloride (SANIZOL B-50.TM.), utilizing a high shearing device, such as a Brinkmann Polytron, microfluidizer or sonicator or using a predispersed pigment comprised of submicron pigment particles stabilized by a nonionic dispersant or grinding aids, to which a cationic surfactant, such as benzalkonium chloride (SANIZOL B.TM.), and water is added; thereafter, shearing such a mixture with a latex of suspended resin particles, such as poly(styrene butadiene acrylic acid), poly(styrene butylacrylate acrylic acid) or PLIOTONE.TM., a poly(styrene butadiene), and which particles are, for example, of a size ranging from about 0.01 to about 0.5 micron in volume average diameter as measured by the Brookhaven nanosizer in an aqueous surfactant mixture containing an anionic surfactant, such as sodium dodecylbenzene sulfonate, for example NEOGEN R.TM. or NEOGEN SC.TM., and a nonionic surfactant such as alkyl phenoxy poly(ethylenoxy)ethanol, for example IGEPAL 897.TM. or ANTAROX 897.TM., using high shearing devices, thereby resulting in a flocculation, or heterocoagulation of the resin particles with the pigment particles; and which, on further stirring for about 1 to about 3 hours while heating, for example, from about 40 to about 50.degree. C., results in the formation of electrostatically bound aggregates ranging in size of from about 0.5 micron to about 10 microns in average diameter size as measured by the Coulter Counter (Microsizer II), where the size of the aggregated particles and their distribution obtained is controlled by the addition of an aqueous suspension submicron in situ tricalcium phosphate (TCP) particulants during the subsequent coalescence where the temperature is raised to 5 to 50.degree. C. above the resin Tg to provide particle fusion or coalescence of the polymer and pigment particles; followed by the addition of acid, such as nitric acid, to dissolve the TCP from the surface of the coalesced toner particle, followed by washing with water and drying whereby toner particles comprised of resin and pigment with various particle size diameters can be obtained, such as from 1 to about 15, and preferably in the range of 2 to 10 microns in average volume particle diameter. The aforementioned toners are especially useful for the development of colored images with excellent line and solid resolution, and wherein substantially no background deposits are present.
While not being desired to be limited by theory, it is believed that the flocculation or heterocoagulation is caused by the neutralization of the pigment mixture containing the pigment and ionic, such as cationic, surfactant absorbed on the pigment surface with the resin mixture containing the resin particles and anionic surfactant absorbed on the resin particle. The particle size obtained during the aggregation step, which comprises heating the mixture below the resin Tg, is controlled by temperature of the aggregation step. Tricalcium phosphate, for example, added at from about 5 to about 50.degree. C. above the resin Tg fuses the aggregated particles or coalesces the particles to enable the formation of toner particles comprised of polymer, pigments and optional toner additives like charge control agents, and the like, such as waxes. Furthermore, in other embodiments the ionic surfactants can be exchanged such that the pigment mixture contains the pigment particle and anionic surfactant, and the suspended resin particle mixture contains the resin particles and cationic surfactant; followed by the ensuing steps as illustrated herein to enable flocculation by charge neutralization while shearing, and thereby forming statically bounded aggregate particles by stirring and heating below the resin Tg; and thereafter, that is when the aggregates are formed, heating above the resin Tg to form stable toner composite particles. The latex blend or emulsion is comprised of resin or polymer, counterionic surfactant, and nonionic surfactant. In the embodiments of the present invention, the amount of the submicron in situ tricalcium phosphate particulant stabilizer selected to retain the particle size and GSD from the aggregation step through the coalescence step is in the range of 0.1 to 5.0 weight percent by weight of the total reactor contents, and preferably in the range of 0.8 to 2.0 weight percent by weight of total reactor contents.
The process described in the present application has several advantages as indicated herein including in embodiments the effective preparation of small toner particles with narrow particle size distribution as a result of no classification; high toner yields; large amounts of power consumption are avoided; the process can be completed in rapid times, including shorter coalescence times; and the process is controllable since the particle size of the toner can be rigidly controlled by, for example, controlling the temperature of the aggregation.
Furthermore, the present invention is directed to the use of a solid particulate as a stabilizer to retain the particle size and the GSD of the aggregates comprised of resin and pigment particles and optional additives, which when heated 5 to 50.degree. C. above the resin Tg, provide pigmented composite toner particles. The toners particles can be washed with dilute nitric acid to dissolve the TCP stabilizer, followed by 2 to 3 washes with water, compared to the 6 to 7 washes usually needed for the surfactant stabilized systems as described in U.S. Pat. No. 5,403,693, the disclosure of which is totally incorporated herein by reference. The present invention thus focuses on the use of solid particulate stabilizers in the aggregation coalescence steps wherein the stabilizer is introduced after the formation of the desired aggregate particle size and GSD, which aggregates are comprised of a resin and a pigment and optional additives, where the aggregates are then further heated to coalesce the aggregates resulting in composite particles, while retaining the particle size and the GSD. Furthermore, with the present invention in embodiments the amount of stabilizer selected is proportional to the particle size required, wherein the smaller the particle size, the greater the amount of the stabilizer. The pigment particles in the size range of about 0.05 to about 0.3 micron are dispersed in a cationic surfactant, and blended with the anionic latex particle, also in the size range of about 0.05 to about 0.3 micron at speeds of 500 to 10,000 rpm and preferably in the range of 1,000 to 5,000 rpm, followed by raising the temperature of the blend to about 5 to 15.degree. C. below the resin Tg to form aggregates of pigment and resin in the size range of 2 to 10 microns with a narrow particle size distribution. There is then added an aqueous in situ submicron TCP particulate generated by mixing an aqueous solution of calcium chloride and trisodium phosphate at speeds of 3,000 to 10,000 rpms. The amount of TCP particulate selected is in the range of 0.1 to 5.0 weight percent based on total reactor contents, and preferably 0.8 to 2.3 weight percent.
There is illustrated in U.S. Pat. No. 4,996,127 a toner of associated particles of secondary particles comprising primary particles of a polymer having acidic or basic polar groups and a coloring agent. The polymers selected for the toners of the '127 patent can be prepared by an emulsion polymerization method, see for example columns 4 and 5 of this patent. In column 7 of this '127 patent, it is indicated that the toner can be prepared by mixing the required amount of coloring agent and optional charge additive with an emulsion of the polymer having an acidic or basic polar group obtained by emulsion polymerization. Also, see column 9, lines 50 to 55, wherein a polar monomer, such as acrylic acid, in the emulsion resin is necessary, and toner preparation is not obtained without the use, for example, of acrylic acid polar group, see Comparative Example I. In U.S. Pat. No. 4,983,488, there is disclosed a process for the preparation of toners by the polymerization of a polymerizable monomer dispersed by emulsification in the presence of a colorant and/or a magnetic powder to prepare a principal resin component, and then effecting coagulation of the resulting polymerization liquid in such a manner that the particles in the liquid after coagulation have diameters suitable for a toner. It is indicated in column 9 of this patent that coagulated particles of 1 to 100, and particularly 3 to 70, are obtained. This process is thus directed to the use of coagulants, such as inorganic magnesium sulfate, which results in the formation of particles with a wide GSD. In U.S. Pat. No. 4,797,339, there is disclosed a process for the preparation of toners by resin emulsion polymerization, wherein similar to the '127 patent certain polar resins are selected, and wherein flocculation as in the present invention is not believed to be disclosed; and U.S. Pat. No. 4,558,108 discloses a process for the preparation of a copolymer of styrene and butadiene by specific suspension polymerization. Other prior art that may be of interest includes U.S. Pat. Nos. 3,674,736; 4,137,188 and 5,066,560.
There is illustrated in U.S. Pat. No. 5,278,020, the disclosure of which is totally incorporated herein by reference, a process for the preparation of a toner composition comprising the steps of
Emulsion/aggregation processes for the preparation of toners are illustrated in a number of Xerox patents, the disclosures of which are totally incorporated herein by reference, such as U.S. Pat. No. 5,290,654, U.S. Pat. No. 5,278,020, U.S. Pat. No. 5,308,734, U.S. Pat. No. 5,346,797, U.S. Pat. No. 5,370,963, U.S. Pat. No. 5,344,738, U.S. Pat. No. 5,403,693, U.S. Pat. No. 5,418,108, U.S. Pat. No. 5,364,729, and U.S. Pat. No. 5,346,797.